THE INTERSTITIAL WATER COMPOSITION IN THE SEDIMENTS OF THE GREAT LAKES.

Four stations in the western end of Lake Ontario were cored and the interstitial water together with the water lying immediately above it were analyzed for the major ions, soluble reactive phosphate, nitrate, silica, iron, and manganese. The interstitial waters are enriched relative to lake waters in all components except chloride, fluoride and sodium and strongly depleted with respect to sulfate. The Eh was generally negative and the pH was around 7.4. No changes from May to August could be observed, but in most cases, silica, alkalinity, manganese, and iron increased with depth in the sediment; chloride, fluoride, sulfate, sodium, and calcium decreased and the other parameters remained more or less constant. The major factors governing the chemistry of the interstitial waters are diffusion, bacterial reduction of sulfate, and equilibrium with various minerals in the sediments. There is evidence that the iron concentration is governed by FeC03 but no firm conclusions could be drawn concerning manganese. For the first phase of a program to study the chemistry of the interstitial waters of lake sediments, a location was chosen where environmental changes were small so that the variation due to sampling could be estimated and some idea obtained about the homogeneity of the lake bottom. The western end of Lake Ontario fulfills these conditions. In 1969, the temperature in-creased from about 2°C in the middle of April to around 4OC in September, although at station 1 (see Fig. 1) the temperatures were always slightly higher. The oxygen saturation was lOO-105 % at the beginning of the period, and it had decreased to only about 80-85 % by September, with station 1 having the lowest values. I wish to thank H. Saitoh, R. Coker, and the Water Quality Division of the Inland Waters Branch for doing the chemica